Cathode-focused research has been carried out to increase the performance of a lithium ion secondary battery comprising an electrolyte and an anode, the electrolyte being an electrolytic solution of a lithium salt dissolved in a solvent, and the anode being a material that can occlude and release lithium (e.g., a carbonaceous material).
For example, Patent Literature 1 discloses an organic liquid electrolyte secondary cell that is capable of, due to incorporation of a phosphate compound (e.g., lithium phosphate) in the positive electrode, preventing electrochemical decomposition of the organic liquid electrolyte when the cell is subject to supercharging, and preventing a rapid increase in the internal pressure of the cell and/or an abnormal increase in the temperature of the cell.
Patent Literature 2 discloses that decomposition of an electrolysis solution can be suppressed by depositing a lithium compound (lithium phosphate) on the surface of a lithium nickel oxide used as a positive electrode active material.
Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 1998-154532
Patent Literature 2: JP-A No. 2005-190996
A lithium ion secondary battery comprising a cathode containing the phosphoric acid compound disclosed in Patent Literature 1 or 2, has a problem of low capacity retention rate.